Isshuukan Friends.

Synopsis

On the very last day of Summer break, Yuki, Kaori, Shogo and Saki get together at Kaori's house to complete their homework assignments. As the day progresses, Shiho explains the positive impact Yuki's friendship has had on Kaori's life and Shogo reaffirms to Yuki on the importance of the process in helping Kaori through her condition. Afterwards, Saki decides to head home despite not finishing her assignments and Shogo lends her his completed answer sheet which triggers a memory from their elementary school where he had also done this for her in the past. After Yuki finally finishes his assignments, he inquires about Kaori's gradually improving memories to which she positively regards their friendship as being the cause. The second semester begins the next day and Inoue refreshes the class's assigned seating which results in Kaori and Yuki seated next to each other. Afterwards Inoue introduces a transfer student named Hajime Kujo, who finds a seat next to Kaori and upon noticing her, harshly brands her as a traitor for breaking their "promise." This causes Kaori to collapse from sudden mental stress and when she finally awakens in the nurse's office, her memories of Yuki are completely reset once more.

(Source: Wikipedia)